Loop heat pipe

ABSTRACT

A loop heat pipe for heat dissipating to a heat source including a first pipe, a first capillary structure, a second capillary structure, a second pipe, and a working fluid is provided. The first pipe has an evaporating portion adjacent to the heat source and a condensing portion. The first capillary structure is disposed on an inner surface of the first pipe and extends from the evaporating portion to the condensing portion. The second capillary structure is disposed on the inner surface and located within the evaporating portion. The second pipe is connected between the evaporating portion and the condensing portion. The working fluid disposed in the first pipe and the second pipe is capable of being transferred from the evaporating portion to the condensing portion via the second pipe, and is capable of being transferred from the condensing portion to the evaporating portion in the first.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 97123967, filed on Jun. 26, 2008. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a heat pipe, and moreparticularly, to a loop heat pipe.

2. Description of Related Art

Along with the rapid developments of computers, communication,information and the relevant industries in recent years, the electronicproducts and the electronic components are designed more following thelight-slim-short-small tendency, which leads to gradually increasing thegenerated heat and the heat density therewithin. To solve the problemsin this regard, a heat pipe device based on the phase transitionprinciple has been broadly used.

FIG. 1 is a structure diagram of a conventional heat pipe. Referring toFIG. 1, a heat pipe 100 includes a closed metallic pipe 110, a capillarystructure 120 disposed on the inner wall of the metallic pipe 110 and aworking fluid disposed in the metallic pipe 110 and in the intersticesof the capillary structure 120. The capillary structure 120 herein isfabricated by sintered body made of metal powder.

When a heated end of the metallic pipe 110 contacts a heat source, theheat of the heat source is transferred into the capillary structure 120via the metallic pipe 110 so as to evaporate the working fluid in liquidstate in the interstices of the capillary structure 120. At the time,the working fluid in liquid state in the interstices of the capillarystructure 120 durably flows from a cooling end of the metallic pipe 110to the heated end thereof due to capillarity, and the working fluid ingas state durably flows towards the cooling end of the metallic pipe 110via the hollow portion of the metallic pipe 110.

Meanwhile, the heat of the working fluid in gas state located at thecooling end is dissipated out of the metallic pipe 110 via the pipe wallthereof. As a result, the working fluid in gas state located at thecooling end is gradually condensed in the interstices of the capillarystructure 120. In this way, the heat pipe 100 dissipates the heat of theheat source through the phase transition and flowing of the workingfluid.

Note that during the heat pipe 100 dissipates the heat of the heatsource, the working fluid in gas state and the working fluid in liquidstate respectively have a flowing direction opposite to each other.Therefore, the working fluid flowing in the metallic pipe 110 encountersa larger resistance. On the other hand, it is known that the heat pipe100 disposed inside an electronic device is usually bent or flattened inthe process thereof to fit the internal space of the electronic device,which likely destroys the capillary structure 120 and accordinglyprevents the working fluid in liquid state from smoothly flowing in theinterstices of the capillary structure 120 due to poor capillarity.

FIG. 2 is a structure diagram of a conventional loop heat pipe.Referring to FIG. 2, a loop heat pipe 200 includes an evaporator 210, aconnection pipe 220 to form a closed loop together with the evaporator210, a condenser 230 disposed on the connection pipe 220 and a workingfluid suitable for flowing in the evaporator 210 and the connection pipe220. The evaporator 210 includes an outer pipe 212, an inner pipe 214disposed in the outer pipe 212 and having a plurality of capillarystructures, a liquid channel 216 formed in the inner pipe and a vapourchannel 218 formed between the outer pipe 212 and the inner pipe 214.

The working fluid in liquid state in the liquid channel 216 can beinfiltrated into the vapour channel 218 via the capillary structures ofthe inner pipe 214 and converted into gas state by absorbing the heatenergy of the heat source. Then, the working fluid in gas state flowsinto the connection pipe 220 via the vapour channel 218. After that, theworking fluid in gas state flowing in the connection pipe 220 is cooledby a condenser 230, converted into liquid state and refluxes back to theevaporator 210. In this way, the working fluid functions to durablydissipate heat on the heat source.

In the loop heat pipe 200, the flowing directions of the working fluidin gas state and the working fluid in liquid state are almost the same,so that the working fluid in liquid state in the connection pipe 220flows towards the evaporator 210 through the capillarity, and theworking fluid in gas state during flowing due to a pressure differenceis able to further push on the working fluid in liquid state forflowing. In comparison with the heat pipe 100, the working fluid in theloop heat pipe 200 encounters a less resistance during flowing.

Although the working fluid in the loop heat pipe 200 encounters a lessresistance during flowing, however, the working fluid in gas state afterpassing the condenser 230 must be completely condensed into the workingfluid in liquid state so as to be refluxed back to the evaporator 210through the capillarity. And in this way, the loop heat pipe 200 is ableto durably dissipate heat on the heat source through the phasetransition and the flowing of the working fluid. In addition, incomparison with the heat pipe 100, it is more difficult to control theheat balance and the working temperature of the loop heat pipe 200.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a loop heat pipe witha better heat transfer efficiency and higher operation stability.

The present invention provides a loop heat pipe suited for heatdissipating to a heat source. The loop heat pipe includes a first pipe,a first capillary structure, a second capillary structure, a second pipeand a working fluid. The first pipe has an evaporating portion and acondensing portion, wherein the evaporating portion is adjacent to theheat source. The first capillary structure is disposed on an innersurface of the first pipe and extends from the evaporating portion tothe condensing portion. The second capillary structure is disposed onthe inner surface and located in the evaporating portion. The secondpipe is connected between the evaporating portion and the condensingportion. The working fluid is disposed in the first pipe and the secondpipe, wherein the working fluid is capable of being transferred from theevaporating portion to the condensing portion through the second pipeand is capable of being transferred from the condensing portion to theevaporating portion in the first pipe.

In an embodiment of the present invention, the above-mentioned firstcapillary structure is a plurality of grooves formed on the innersurface, and the above-mentioned second capillary structure is asintering structure.

In an embodiment of the present invention, the above-mentioned firstcapillary structure and second capillary structure are formed as anintegrative sintering structure.

In an embodiment of the present invention, the above-mentioned secondcapillary structure has an exhaust end and a reflux end, and the heatsource and the second pipe are adjacent to the exhaust end.

In an embodiment of the present invention, the above-mentioned exhaustend is an open end and the above-mentioned reflux end is a close end.

In an embodiment of the present invention, the thickness of theabove-mentioned exhaust end is less than the thickness of the refluxend.

In the loop heat pipe of the present invention, the flowing directionsof the working fluid in liquid state and the working fluid in gas stateare almost the same; therefore, the working fluid flowing in the firstpipe and the second pipe encounters a less resistance. In addition, theworking fluid in gas state after passing the condensing portion is notrequired to be completely converted into the working fluid in liquidstate. In other words, the working fluid flowing from the condensingportion towards the evaporating portion in the first pipe can be in aliquid-gas coexistence status. Therefore, the heat balance and theworking temperature of the invented loop heat pipe are easier to becontrolled.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a structure diagram of a conventional heat pipe.

FIG. 2 is a structure diagram of a conventional loop heat pipe.

FIG. 3 is a structure diagram of a loop heat pipe according to anembodiment of the present invention.

FIG. 4 is the sectional view along A-A line in FIG. 3.

FIG. 5 is the sectional view along B-B line in FIG. 3.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIG. 3 is a structure diagram of a loop heat pipe according to anembodiment of the present invention. Referring to FIG. 3, a loop heatpipe 300 is suited for heat dissipating to a heat source, wherein theheat source is, for example, a central processing unit (CPU) or otherelectronic components. The loop heat pipe 300 includes a first pipe 310,a first capillary structure 320, a second capillary structure 330, asecond pipe 340 and a working fluid.

Both opposite ends of the first pipe 310 are respectively an evaporatingportion 312 and a condensing portion 314, wherein the evaporatingportion 312 is adjacent to the heat source. The first capillarystructure 320 is disposed on an inner surface of the first pipe 310 andextends from the evaporating portion 312 to the condensing portion 314.The second capillary structure 330 is disposed on the inner surface andlocated in the evaporating portion 312. The second pipe 340 is connectedbetween the evaporating portion 312 and the condensing portion 314, andthe working fluid is suited for flowing in the first pipe 310 and thesecond pipe 340.

In more detail, the heat produced by the heat source can be transferredinto the first capillary structure 320 and the second capillarystructure 330 of the evaporating portion 312 via the first pipe 310 soas to evaporate the working fluid in liquid state located in the firstcapillary structure 320 and the second capillary structure 330.Meanwhile, the working fluid in gas state located in the condensingportion 314 is cooled and then condensed into liquid on the innersurface of the first pipe 310. As a result, the working fluid in gasstate located in the evaporating portion 312 would be graduallyincreased and the working fluid in gas state located in the condensingportion 314 would be gradually decreased. In this way, the working fluidin gas state is able to flow from the evaporating portion 312 to thecondensing portion 314 through the second pipe 340 due to a pressuredifference; meanwhile, the working fluid in liquid state is able todurably flow in the interstices of the first capillary structure 320from the condensing portion 314 towards the evaporating portion 312 dueto capillarity; and the loop heat pipe 300 of the present inventionfunctions to durably dissipate heat on the heat source through the phasetransition and the flowing of the working fluid.

Note that the working fluid in liquid state flows in the interstices ofthe first capillary structure 320 from the condensing portion 314towards the evaporating portion 312 through capillarity. Therefore, thepartial working fluid in gas state which is not yet condensed intoliquid state in the condensing portion 314 can flow from the condensingportion 314 towards the evaporating portion 312 in a hollow portion 316of the first pipe 310. In other words, even though the working fluid ingas state is not completely condensed into the working fluid in liquidstate in the condensing portion 314, but the invented loop heat pipe 300can still durably dissipate heat on the heat source; and thereby, incomparison with the conventional loop heat pipe 200, the heat balanceand the working temperature of the invented loop heat pipe 300 is easierto be controlled.

Additionally, the working fluid in gas state and the working fluid inliquid state in the loop heat pipe 300 of the present invention havealmost the same flowing directions; thus, the working fluid in liquidstate is able to durably flow in the interstices of the first capillarystructure 320 from the condensing portion 314 towards the evaporatingportion 312 not only through capillarity, but also by the assistance ofthe working fluid in gas state which is able to push on the workingfluid in liquid state for flowing when the working fluid in gas stateflows in the hollow portion 316 of the first pipe 310 from thecondensing portion 314 towards the evaporating portion 312. Accordingly,in comparison with the conventional heat pipe 100, the working fluid ofthe invented loop heat pipe 300 encounters a less resistance duringflowing in the first pipe 310.

FIG. 4 is the sectional view along A-A line in FIG. 3 and FIG. 5 is thesectional view along B-B line in FIG. 3. Referring to FIGS. 3 and 4, inthe embodiment, the first pipe 310 is, for example, a pipe with grooves,and the first capillary structure 320 is just the plurality of groovesformed on the inner surface of the first pipe 310. The second pipe 340is, for example, a smooth pipe which enables the working fluid in gasstate flowing in the second pipe 340 to have a better flowingefficiency. In other unshown embodiments, the first pipe 310 and thesecond pipe 340 can be formed as an integrative pipe with grooves so asto shorten the process of the loop heat pipe 300.

Referring to FIGS. 3 and 5, the second capillary structure 330 hereinis, for example, a tubular sintering structure formed on the innersurface of the first pipe 310; especially, the second capillarystructure 330 can be formed by sintering metal powder. In addition, thesecond capillary structure 330 can have an exhaust end E and a refluxend I, and the heat source is adjacent to the exhaust end E.

Note that the thickness of the exhaust end E is made less than thethickness of the reflux end I when forming the second capillarystructure 330; that is to say the remaining inner diameter of the secondcapillary structure 330 at the exhaust end E is greater than theremaining inner diameter thereof at the reflux end I. In this way, theworking fluid in gas state located in the evaporating portion 312 has aless resistance during passing the exhaust end E than that duringpassing the reflux end I. Therefore, when the working fluid in gas statelocated in the evaporating portion 312 is gradually increased, theworking fluid in gas state flows almost towards the second pipe 340,which avoids the working fluid in gas state and the working fluid inliquid state in the first pipe 310 from flowing towards two directionsopposite to each other.

On the other hand, the heat source in the embodiment is more close tothe exhaust end E than the reflux end I so that the working fluid inliquid state at the exhaust end E has a greater evaporation rate thanthat at the reflux end I. When the remaining inner diameter of thesecond capillary structure 330 at the reflux end I is extremely small,the hole with the extremely small diameter at the reflux end I may befilled up with the working fluid in liquid state accumulated in theinterstices of the second capillary structure 320, which further avoidsthe working fluid in gas state and the working fluid in liquid state inthe first pipe 310 from flowing towards two directions opposite to eachother.

In other unshown embodiments, the exhaust end E can be an open end andthe reflux end I can be a close end, which forces the working fluid ingas state in the evaporating portion 312 flowing towards the second pipe340 only.

Note that the first capillary structure 320 in the embodiment is aplurality of grooves formed on the inner surface of the first pipe 310;thus, even though a user makes the first pipe 310 bent or flattened inthe process thereof, the working fluid in liquid state is still able toflow basically in the grooves through capillarity. In comparison withthe conventional heat pipe 100, the loop heat pipe 300 of the presentinvention is more suitable to be re-processed to fit the assembly space.

In addition, in other unshown embodiments, where the loop heat pipe 300is not bent or flattened in the processing thereof, the first capillarystructure 320 and the second capillary structure 330 can be formed as anintegrative sintering structure.

In summary, in the loop heat pipe of the present invention, the workingfluid in liquid state and the working fluid in gas state have almost thesame flowing directions, so that the working fluid in liquid state flowsnot only through capillarity, but also by the assistance of the flowingworking fluid in gas state which is able to push on the working fluid inliquid state for flowing. Thus, in comparison with the heat pipe in theprior art, the working fluid in the loop heat pipe of the presentinvention encounters a less resistance in flowing.

Furthermore, when the working fluid passes through the condensingportion, the working fluid condensed into liquid state can flow throughcapillarity in the interstices of the first capillary structure from thecondensing portion towards the evaporating portion, while the restworking fluid in gas state can flow in the hollow portion of the firstpipe from the condensing portion towards the evaporating portion.Therefore, even though the working fluid in gas state is not yetcompletely condensed into liquid state in the condensing portion, theloop heat pipe of the present invention still can durably dissipate heaton the heat source; and in comparison with the conventional heat pipe,the heat balance and the working temperature of the invented loop heatpipe is easier to be controlled.

Moreover, the loop heat pipe of the present invention can take astructure with grooves to replace a part of the sintering structure, sothat even though a user makes the first pipe bent or flattened in theprocess thereof, the working fluid in liquid state is able to flowbasically in the grooves through capillarity. In comparison with theconventional heat pipe, the loop heat pipe of the present invention ismore suitable to be re-processed to fit the assembly space.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A loop heat pipe, suitable for heat dissipating to a heat source; theloop heat pipe comprising: a first pipe, having an evaporating portionand a condensing portion, wherein the evaporating portion is adjacent tothe heat source; a first capillary structure, disposed on an innersurface of the first pipe and extending from the evaporating portion tothe condensing portion; a second capillary structure, disposed on theinner surface and located in the evaporating portion; a second pipe,connected between the evaporating portion and the condensing portion;and a working fluid, disposed in the first pipe and the second pipe,wherein the working fluid is capable of being transferred from theevaporating portion to the condensing portion via the second pipe and iscapable of being transferred from the condensing portion to theevaporating portion in the first pipe.
 2. The loop heat pipe accordingto claim 1, wherein the first capillary structure is a plurality ofgrooves formed on the inner surface, and the second capillary structureis a sintering structure.
 3. The loop heat pipe according to claim 1,wherein the first capillary structure and the second capillary structureare formed as an integrative sintering structure.
 4. The loop heat pipeaccording to claim 1, wherein the second capillary structure has anexhaust end and a reflux end, and the heat source and the second pipeare adjacent to the exhaust end.
 5. The loop heat pipe according toclaim 4, wherein the exhaust end is an open end and the reflux end is aclose end.
 6. The loop heat pipe according to claim 4, wherein thethickness of the exhaust end is less than the thickness of the refluxend.